As well-known an ion implantation is utilized to perform an impurity doping or a material synthesization on a substrate by irradiating an accelerated ion onto the surface thereof. The doping can be performed without any influence of the surface condition of the substrate and with very high accuracy and cleanliness. Therefore, the ion implantation is utilized for manufacturing LSI elements, VLSI elements or the like, or synthesizing an alloy or an amorphous material.
A conventional ion implanter system is shown in FIG. 1 of the accompanying drawings, in which it comprises an ion source A, a mass spectrometer having an analyzer magnet and intended to take out ions having a predetermined kinetic energy and mass from other ions produced in the ion source A, an acceleration system having an acceleration tube C for accelerating the ions taken out by the mass spectrometer, a converging lens system D, a deflector/scanner system having Y direction scanning electrode E and X direction scanning electrode F, and a sample processing chamber which contains a sample to be ion implanted.
In the ion implanter system it is important that the scanning system should be constructed to eliminate neutral particles in order to improve the uniformity of the doping. The neutral particles are generated by colliding the ion beams with residual gas molecules while the ion beams from the ion source are transmitted to the sample and making the charge exchange therebetween. The ion implanter system is therefore provided with means for deflecting the center line of the beams by 7.degree. to avoid the incidence of the neutral particles on the sample, lest the uniformity should be deteriorated by an enhanced doping at the central portion of the sample with the neutral particles. That is, it is usual to provide a voltage control in the X direction scanning electrode F by superimposing a DC bias for deflecting the ion beams by 7.degree. on a scanning triangular wave for the X direction scanning electrode F.
In the conventional ion implanter systems of parallel plates electrostatic X-Y scanner type, the range of a uniform electric field is narrowed due to a disturbance in the electric field at the edge portion. It is, therefore, necessary to increase the width of the scanner plates and thus the size of the electrodes. The system of this type also has a deflecting distortion considerably increased as well as an increased electric capacity. Since the superimposed deflection voltage for eliminating the neutral particles and the scanning triangular wave voltage are applied to at least one scanning electrode of the deflector/scanner system, the voltage to be applied to the electrode is increased, and thus it is necessary to generate a high voltage. Therefore, the triangular wave voltage becomes obtuse in case of high speed scanning. If the voltage is higher, it is substantially impossible to protect the system from any corona discharge or leakage, which makes it difficult to design a scanning power source. Furthermore, the life-time of a power source is shortened.
On the other hand, as the microfabrication of a wafer progresses and the pattern line width decreases, a shadowing effect in ion implantation becomes a problem. For a CMOS DRAM having 4 M bits memory or more, thus, it is necessary to ion implant the whole surface of a wafer with an ion beam pointed parallel to a definitely predetermined direction. More specifically, as the wafer size is increased from 6 to 8 inches and the memory size of the DRAMs increases to 4 M or further 16 M bits, and thus the pattern width is reduced, the need of parallel ion beam implantation has become to be closed-up. With the conventional raster scan type ion implanter having a pair of deflectors for scanning an ion beam, however, even if a distance between the deflectors and the wafer to be ion implanted is 160 cm, the maximum deflecting angle for a 6-inch wafer becomes .alpha..sub.max =2.7.degree.
In a conventional electrostatic X-Y sweeping type deflector system, an ion beam has a deflection angle except the center portion because the ion beam is raster-scanned in X and Y directions. Thus, when such ion beam is implanted to a flat wafer, an implantation incidence angle difference occurs from point to point. This phenomenon causes a shadowing effect in the ion implantation in fabricating semiconductor devices. Further, the uniformity of the ion implantation is deteriorated at the periphery portion of the wafer where the solid angle of the ion beam cut by unit area of wafer diminishes, also feasibly causing channeling at the periphery portion.
In the conventional system the deflecting angle .theta. is larger at the periphery portion than at the center portion of the wafer, and the depth of the ion implantation in the wafer is shallower at the periphery portion than at the center portion thereof because it is determined by the vertical component of the velocity of implanted ion. As a result, the uniformity of doping is deteriorated. If it is intended to restrain the deflecting angle .theta. within a predetermined level upon the ion implantation for a wafer having a larger diameter, it is necessary to lengthen the ion beam transmitting system, and thus the whole system is enlarged, thereby increasing the floor area of the machine and the manufacturing cost of products.
As the memory size of DRAM increases to 4 M or 16 M bits the trench construction is inevitable, and the microfabrication of a wafer involves the increasing of an aspect ratio of trenches. If the ion implantation is performed on the bottom of a trench having a large aspect ratio, it is impossible to obtain a uniform ion implanting all over the bottom surface by using the ion beam with a deflection angle .theta.. This difficulty may be reduced to a certain extent by carrying out the ion implantation while the wafer is rotated, but cannot fully be overcome. When the ion implantation is made on the side wall(s) of the trench, the wafer is inclined in correspondence with the aspect ratio of the trench in order to avoid shadowing. It is, however, difficult to obtain a uniform ion implantation on the side wall. When the ion beam is implanted obliquely on the side wall of the trench, there may appear a portion of the side wall on which the ion implantation is not carried out.
Then, there has been proposed a parallel sweeping system for implanting ions to a wafer from a definitely predetermined direction by using two sets of parallel plates electrostatic deflectors, in which the ion beam is deflected by .alpha..degree. by the first electrostatic deflector, run at a distance L and then again deflected by -.alpha..degree. by the second electrostatic deflector.
In the above-mentioned parallel plates deflector systems, the available region is narrowed due to the disturbance of the electric field at the edge portion. The width of the parallel plates scanner is necessitated to be at least 2 W for its gap of W, considering the half gap disturbance of the field at both edges. In the deflector of the rear stages, there arise drawbacks that it has an increased electric capacity, the triangular wave voltage becomes obtuse ordinary scanning, and it becomes difficult to design a scanning power supply.
It is, therefore, an object of the present invention to overcome the problems of nonuniformity of an ion implantation in a target due to the increasing of the diameter thereof and of a shadowing due to the trench construction.
Another object of the present invention is to provide an ion implanter system in which a target can be swept by a parallel scanning beam which is incident all over the target at the same incident angle.
Another object of the present invention is to provide an ion implanter system in which a deflector/scanner system comprises a separated deflecting section and scanning section, and the scanning section include electrodes having a broad effective region and a small deflecting distortion.
A further object of the present invention is to provide an ion implanter system which is capable of providing a parallel scanning ion implantation of a target.